JP3882041B2 - Method for evaluating corrosion resistance of coating film - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The invention of this application relates to a method for evaluating corrosion resistance of a coating film, and more particularly to a method for evaluating corrosion resistance of a coating film including a technique for identifying a new scratch on the coating film.
[0002]
[Prior art and its problems]
The corrosion mechanism under the paint film has been studied mainly by the impedance method. However, since the resistance is too high in a very thick coating, the impedance cannot be measured.
[0003]
The inventors first developed a portable rust change stabilization measurement device and evaluated the degree of rust stabilization from the change in surface potential, but evaluated it in the short term for the corrosion resistance of coatings actually used such as heavy paint. However, there was a problem in elucidating the corrosion mechanism.
[0004]
Under such circumstances, the invention of this application is based on the fact that the present invention is applicable to short-term evaluation of corrosion resistance of coatings actually used such as heavy coating and to elucidate the corrosion mechanism. I found a method to monitor Specifically, this is because the surface potential was stabilized by leaving it in a state where it can be measured for several days before the measurement, and then the initial corrosion damage can be measured by performing a corrosion test.
[0005]
Until now, the surface potential of metal materials has been measured before a small amount of moisture is attached to the rust generated on the surface, from the point of attachment until it is dried, and the degree of rust stabilization is evaluated from the potential fluctuation. There is also an invention (Patent No. 3277223), but there is no evaluation of the coating film by surface potential, and there is no method for monitoring the initial corrosion under the coating of thick paint as in the present invention.
[0006]
[Means for Solving the Problems]
In order to solve the above problems, the invention of this application removes a part of the coating film provided on the metal plate to expose the metal surface, stabilizes the potential of the metal surface, and then exposes the exposed metal. Measure the change in surface potential over time, and if there is a potential change and the potential change does not disappear, it is determined that the coating film has scratches that reach the metal surface, and the potential changes gradually disappear. In some cases, the coating surface corrosion resistance evaluation method is characterized by monitoring the presence of coating film scratches that have not reached the metal surface, but the coating film scratches are formed, and the corrosion damage of the metal due to the coating film scratches ( Claim 1) is provided.
[0008]
According to the present invention, a coating film used in the vicinity of the coast can contribute to the development of a new coating film based on the evaluation of corrosion resistance in a short time.
[0009]
The invention of this application has the features as described above, and the embodiments thereof will be described below.
[0010]
DETAILED DESCRIPTION OF THE INVENTION
In the invention of this application, a very small scratch is first applied to the coating film, and the initial coating film scratch can be determined from the potential change.
[0011]
A minute scratch that exposes the metal surface is made, and magnesium chloride droplets are attached to a place where the scratch is made and a place where the scratch is not made, and the corrosion portion can be determined from the difference in potential behavior.
[0012]
Even when the humidity is changed, the wettability of the coating film / metal interface can be determined based on the presence or absence of potential fluctuation when the humidity is changed.
[0013]
【Example】
Example 1
In order to obtain the surface potential distribution of the coating film, it is necessary to expose the metal part in order to take the ground.
[0014]
Here, it was found that the surface potential was stabilized when the metal part was exposed and left in the measurement state for one day. Therefore, the surface potential was stabilized, and then, as shown in FIG. 2, a scratch having a width of 0.1 mm, a depth of 0.03 mm, and a length of 1.5 mm was first applied to a film having a thickness of 0.1 mm with a cutter. Attached to the membrane surface.
[0015]
And the electric potential distribution was measured from the time immediately after passing through immediately after scratching the coating-film surface of a metal with a coating film.
[0016]
FIG. 3 shows a laser microscope image and a change in potential over time when a very small scratch of the above-described conditions is applied to the coating film surface. 3 (a), (b), and (c), the interval between the right column potentials is expressed in units of 0.25V. In this case, the scanning range is 20 mm × 20 mm.
[0017]
Fig. 3 (a) shows the change in surface potential distribution immediately after a new scratch on the coating film, (b) shows the change in surface potential distribution two hours after scratching the coating film, and (c) shows the change in surface potential distribution. The graph shows changes in the surface potential distribution after 5 hours from scratching the membrane. According to this, it can be seen that the potential change of the scratched portion gradually disappears as time elapses from FIG. 3 (a) → (b) → (c).
[0018]
Further, as shown in FIG. 4, a scratch having a width of 0.5 mm, a depth of 0.12 mm, and a length of 3 mm is applied so that the metal part is exposed, and 1 μl of a magnesium chloride solution is adhered to cause corrosion. It was.
[0019]
As a result, a potential change was observed and it was found that very small corrosion was detectable.
[0020]
FIG. 5 shows a potential change and a color laser microscope image of the defect when an artificial defect is made in the coating film and corroded. In FIGS. 5A, 5B, and 5C, current changes at equal intervals in the right column are expressed in units of 0.2V. In this case, the scanning range is 20 mm × 20 mm.
[0021]
FIG. 5A shows the change in the surface potential distribution of the artificial defect made on the coating film before the corrosion test, FIG. 5B shows the change in the surface potential distribution immediately after the corrosion test, and FIG. 5C shows one hour after the corrosion test. FIG. 5 shows changes in the distribution of the surface potential after the lapse of time, and during the passage of time of FIG. 5 (a) → (b) → (c), the potential change occurs during the corrosion and disappears. In this case, information is enlarged and displayed even though the corroded portion is very small.
[0022]
On the other hand, a similar corrosion test experiment was performed on a portion having no defect, but no change in potential was observed.
[0023]
From the above, as shown in FIG. 1, it is possible to detect whether there is a change with time by measuring a potential change, and when there is no change, it can be determined that there is no defect in the coating film. When there is a potential change and the potential change does not disappear , it can be determined that a scratch reaching the metal surface is formed on the coating film. On the other hand, if there is a potential change and this disappears gradually, it can be determined that a coating film scratch has been formed although the metal surface has not been reached.
Thus, by detecting I by the behavior of the potential change in the surface potential measurement of the coating, the monitor detects the presence or the coating scratches, corrosion damage to the metal due to the presence of the coating flaws reaching the metal surface It becomes possible to do.
[0024]
In this case, the degree of damage can be detected based on the measured surface potential magnitude, extinction time length, and the like, so that the corrosion resistance of the coating film can be finally evaluated .
[0028]
Moreover, as a result of measuring the potential of a very thick coating used on the beach, it was found that this was possible.
[0029]
In addition, about the dimension of said crack, it is an example, Comprising: It is not limited to those dimensions.
[0030]
【The invention's effect】
From the above, the invention of this application can perform a short-term evaluation of the corrosion resistance of a coating that is actually used even in the case of heavy coating, which has been impossible in the past, and can also be applied to the elucidation of the corrosion mechanism.
[0031]
In addition, the short-term evaluation of the corrosion resistance of the paint enables the development of new corrosion resistant coatings.
[Brief description of the drawings]
FIG. 1 shows a flow diagram of a method for monitoring coating film defects.
FIG. 2 shows an outline of a scratch to be newly applied to the coating surface, (a) shows the shape of the scratch, and (b) shows a laser microscope image of the scratch when a new scratch is applied to the coating surface. .
[Fig. 3] Fig. 3 shows the change in potential over time in a scratch with a new coating surface, (a) is the change in surface potential distribution immediately after a new scratch is applied, and (b) is the surface potential distribution after 2 hours. (C) shows the change in the surface potential distribution after 5 minutes.
FIG. 4 shows an outline of an artificial defect formed by creating a scratch reaching the metal surface further in the coating film, (a) showing the shape of the artificial defect, (b) showing a color laser microscope image immediately before corrosion, (C) shows the color laser microscope image after a corrosion test, respectively.
FIG. 5 shows potential changes when an artificial defect is made in a coating film and corroded. (A) is before the corrosion test, (b) is immediately after the corrosion test, (c) is one hour after the corrosion test. Changes in the surface potential distribution are shown.
FIG. 6 shows a flow diagram of a method for monitoring the wettability of a paint metal coating / metal interface according to the invention of this application.
FIGS. 7A and 7B show changes in surface potential distribution associated with changes in humidity of a hydrophilic coating film. FIG. 7A shows changes in surface potential distribution at a relative humidity of 30, and FIG. 7B shows changes in surface potential distribution at a relative humidity of 80. Show.

Claims (1)

After removing a part of the coating film provided on the metal plate to expose the metal surface and stabilizing the potential of the metal surface, measure the time variation of the exposed metal surface potential, If the potential change does not disappear, it is determined that a scratch reaching the metal surface is formed on the coating, and if the potential change gradually disappears, the coating does not reach the metal surface but the coating scratch is A method for evaluating corrosion resistance of a coating film, characterized by monitoring the presence of coating film scratches that are judged to be formed and the corrosion damage of metals due to coating film scratches.

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